feat: set leader election when single controller deployments are configured

CHANGELOG.md

@@ -108,6 +108,8 @@ Adding a new version? You'll need three changes:
   that all time series for those metrics will get a new label designating the
   address of the dataplane that the configuration push has been targeted for.
   [#3521](https://github.com/Kong/kubernetes-ingress-controller/pull/3521)
+- Leader election is enabled by default then kong admin service discovery is enabled.
+  [#3529](https://github.com/Kong/kubernetes-ingress-controller/pull/3529)
 
 ### Fixed
 

internal/manager/run.go

@@ -16,6 +16,7 @@ import (
 	knativev1alpha1 "knative.dev/networking/pkg/apis/networking/v1alpha1"
 	ctrl "sigs.k8s.io/controller-runtime"
 	"sigs.k8s.io/controller-runtime/pkg/healthz"
+	"sigs.k8s.io/controller-runtime/pkg/manager"
 	gatewayv1alpha2 "sigs.k8s.io/gateway-api/apis/v1alpha2"
 	gatewayv1beta1 "sigs.k8s.io/gateway-api/apis/v1beta1"
 
@@ -168,12 +169,7 @@ func Run(ctx context.Context, c *Config, diagnostic util.ConfigDumpDiagnostic, d
 	if err := mgr.AddHealthzCheck("health", healthz.Ping); err != nil {
 		return fmt.Errorf("unable to setup healthz: %w", err)
 	}
-	if err := mgr.AddReadyzCheck("check", func(_ *http.Request) error {
-		if !synchronizer.IsReady() {
-			return errors.New("synchronizer not yet configured")
-		}
-		return nil
-	}); err != nil {
+	if err := mgr.AddReadyzCheck("check", readyzHandler(mgr, synchronizer)); err != nil {
 		return fmt.Errorf("unable to setup readyz: %w", err)
 	}
 
@@ -206,6 +202,26 @@ func Run(ctx context.Context, c *Config, diagnostic util.ConfigDumpDiagnostic, d
 	return mgr.Start(ctx)
 }
 
+type IsReady interface {
+	IsReady() bool
+}
+
+func readyzHandler(mgr manager.Manager, dataplaneSynchronizer IsReady) func(*http.Request) error {
+	return func(_ *http.Request) error {
+		select {
+		// If we're elected as leader then report readiness based on the readiness
+		// of dataplane synchronizer.
+		case <-mgr.Elected():
+			if !dataplaneSynchronizer.IsReady() {
+				return errors.New("synchronizer not yet configured")
+			}
+		// If we're not the leader then just report as ready.
+		default:
+		}
+		return nil
+	}
+}
+
 func getScheme() (*runtime.Scheme, error) {
 	scheme := runtime.NewScheme()
 

internal/manager/setup.go

@@ -107,6 +107,10 @@ func leaderElectionEnabled(logger logr.Logger, c *Config, dbmode string) bool {
 	}
 
 	if dbmode == "off" {
+		if c.KongAdminSvc.Name != "" {
+			logger.Info("DB-less mode detected with service detection, enabling leader election")
+			return true
+		}
 		logger.Info("DB-less mode detected, disabling leader election")
 		return false
 	}